1. Technical Field of the Invention
The present invention relates generally to tire inflation pressure detecting apparatuses for detecting the inflation pressure of tires on a vehicle and tire location detecting apparatuses for automatically detecting the locations of tires on a vehicle.
More particularly, the invention relates to a direct-type tire inflation pressure detecting apparatus for a vehicle which has a function of identifying running and spare wheels of the vehicle.
2. Description of the Related Art
Conventional direct-type tire inflation pressure detecting apparatuses generally include a plurality of transmitters and a receiver.
Each of the transmitters is directly mounted on one of a plurality of wheels of a vehicle and includes a pressure sensor working to sense the inflation pressure of a tire fitted on the wheel. Each of the transmitters is configured to transmit a pressure signal representative of the inflation pressure of the tire sensed by the pressure sensor.
The receiver is mounted on the body of the vehicle and includes at least one antenna. The receiver is configured to receive the pressure signals transmitted from the transmitters via the antenna and determine the inflation pressure of the tires based on the received pressure signals.
However, in the above arrangement, the receiver may receive, in addition to the pressure signals transmitted by the transmitters, pressure signals transmitted by external transmitters. However, it is impossible for the receiver to determine whether a pressure signal received thereby has been transmitted by one of the transmitters or by an external transmitter. Moreover, it is also impossible for the receiver to detect the locations of the transmitters (or the associated tires) on the vehicle. In other words, the receiver cannot identify the wheel on which the transmitter having transmitted a pressure signal and the tire whose inflation pressure is indicated by the pressure signal are located.
To solve the above problems, as disclosed in U.S. Pat. No. 5,602,524, each of the transmitters may be configured to transmit an identification signal (to be referred to as ID signal hereinafter) representative of the identity thereof along with the pressure signal. On the other hand, the receiver may be configured to have reference ID signals registered therein, each of which coincides with the ID signal of one of the transmitters and is associated with the location of that transmitter.
Thus, the receiver may work to compare an ID signal received thereby with the reference ID signals registered therein and identify the transmitter which has transmitted the ID signal when the ID signal coincides with one of the reference ID signals.
Consequently, the receiver can identify the wheel on which the identified transmitter is mounted. More specifically, the receiver can determine whether the wheel is a FR (front-right), a FL (front-left), a RR (rear-right), or a RL (rear-left) wheel of the vehicle. Further, the receiver can determine the inflation pressure of the tire fitted on the identified wheel based on the pressure signal received along with the ID signal.
However, with such a configuration, it is required to previously register the ID signals specific to the respective transmitters as reference ID signals in the receiver through associating the ID signals with the locations of the respective transmitters on the vehicle (i.e., the wheels on which the respective transmitters are mounted). Moreover, as tire replacement or rotations are performed, it is required to update the reference ID signals in the receiver.
Conventionally, the registration of the ID signals in the receiver is made through performing a time-consuming manual operation. Thus, it is desired to automatically make the ID registration. Further, for automatically making the ID registration, it is desired to automatically detect the locations of the transmitters (or the associated tires), in other words, to automatically identify the wheel on which each of the transmitters (or the associated tires) is mounted.
Moreover, the vehicle wheels generally include a spare wheel that is located on the body of the vehicle in the vicinity of the rear wheels of the vehicle and also has a transmitter mounted thereon. Thus, in automatic detection of the locations of transmitters on the vehicle, it is difficult for the receiver to determine whether a pressure signal received thereby is transmitted by the transmitter on the spare wheel or by the transmitter on one of the rear wheels of the vehicle. In other words, it is difficult for the receiver to identify whether the wheel on which the transmitter having transmitted the pressure signal is mounted is the spare wheel or one of the rear wheels of the vehicle.